U.S. patent number 5,436,074 [Application Number 07/982,055] was granted by the patent office on 1995-07-25 for polypropylene highly spread plexifilamentary fiber.
This patent grant is currently assigned to Asahi Kasei Kogyo Kabushiki Kaisha. Invention is credited to Yoshiaki Nakayama, Kazuhiko Shimura.
United States Patent |
5,436,074 |
Shimura , et al. |
July 25, 1995 |
Polypropylene highly spread plexifilamentary fiber
Abstract
A polypropylene three-dimensional plexifilamentary fiber having
a microwave birefringence of 0.07 or more and an Mw/Mn of 4.3 or
less. Although a spreading agent is not included in this fiber, the
fiber has a superior fiber spreadability and dimensional stability.
The fiber in accordance with the present invention can be spun from
a dope composed of an isotactic polypropylene having an Mw/Mn of
4.3 or less and an MFR of 20 or less, and a halogenated
hydrocarbon, by a flash spinning technique. Further, the present
invention provides a spinning dope and a method of manufacturing
the fiber which effectively prevent ozone layer destruction by
using a 2,2-dichloro-1,1,1-trifluoroethane, a
1,2-dichlorotrifluoroethane or a solvent blended a dichloromethane
with either of the above two solvents as the halogenated
hydrocarbon.
Inventors: |
Shimura; Kazuhiko (Nobeoka,
JP), Nakayama; Yoshiaki (Nobeoka, JP) |
Assignee: |
Asahi Kasei Kogyo Kabushiki
Kaisha (Osaka, JP)
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Family
ID: |
27324522 |
Appl.
No.: |
07/982,055 |
Filed: |
November 25, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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800715 |
Dec 3, 1991 |
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549314 |
Jul 9, 1990 |
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Foreign Application Priority Data
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Jul 12, 1989 [JP] |
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1-178097 |
Jul 28, 1989 [JP] |
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1-194374 |
Aug 8, 1989 [JP] |
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1-203864 |
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Current U.S.
Class: |
428/369; 428/357;
428/400; 428/364; 428/397; 162/157.5; 528/491; 528/502R; 525/333.8;
264/205 |
Current CPC
Class: |
D01D
5/11 (20130101); D01F 6/06 (20130101); Y10T
428/2922 (20150115); Y10T 428/2913 (20150115); Y10T
428/2973 (20150115); Y10T 428/2978 (20150115); Y10T
428/29 (20150115) |
Current International
Class: |
D01F
6/04 (20060101); D01D 5/11 (20060101); D01F
6/06 (20060101); D01D 5/00 (20060101); D01F
006/00 () |
Field of
Search: |
;428/357,364,369,400
;264/205 ;162/157.5 ;525/333.8 ;528/491,502 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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62-33816 |
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Oct 1988 |
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JP |
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88-10330 |
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Jun 1990 |
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WO |
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Other References
Encyclopedia of Polymer Science and Engineering, vol. 15, pp.
347-348 John Wiley & Sons, New York (1988)..
|
Primary Examiner: Lesmes; George F.
Assistant Examiner: Choi; Kathleen L.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner
Parent Case Text
This application is a continuation, of application Ser. No.
07/800,715 filed Dec. 3, 1991, which is a continuation of Ser. No.
07/549,314 filed Jul. 9, 1990, both now abandoned.
Claims
We claim:
1. A polypropylene fibrillated three-dimensional plexifilamentary
fiber of an isotactic polypropylene, wherein said fiber has a
microwave birefringence of 0.07 or more, a Mw/Mn of 4.3 or less,
and a MFR of from 3.5 to 10.
Description
BACKGROUND OF THE INVENTIONS
1. Field of the Invention
The present invention relates to a polypropylene highly spread
plexifilamentary fiber, a dope used for manufacturing the fiber,
and a method of manufacturing the fiber. More particularly, the
present invention relates to a polypropylene plexifilamentary fiber
highly spread to a three-dimensional state and having a high
thermal dimensional stability, a dope including a solvent having a
weak ozone layer depletion potential and used for manufacturing the
fiber, and a method of manufacturing the fiber.
2. Description of the Related Art
A fiber manufactured by a flash spinning technique is known as a
fiber fibrillated in a three-dimensional plexifilamentary state.
The flash spinning technique is a spinning method in which a
uniform solution of a polymer having a fiber-forming ability and a
solvent is instantaneously extruded through a spinneret having one
or more holes, at a temperature higher than a boiling temperature
of the solvent and under a pressure higher than a vapor pressure of
the solvent to an area under a lower pressure. The features of the
fiber are disclosed in U.S. Pat. No. 3,081,519 and Japanese
Examined Patent Application (Kokoku) No. 40-28125.
Namely, the fiber disclosed in U.S. Pat. No. 3,081,519 is a fiber
of an organic synthetic crystalline polymer having a surface area
of 2 m.sup.2 /g or more and a structure in which fibrils are spread
in a three-dimensional plexifilamentary state. The fibril has an
average thickness of 4 .mu. or less and an orientated structure,
and is characterized in that an average orientation angle measured
by an electron diffraction method is 90.degree. or less. Further
this fiber is characterized in that an average orientation angle
measured by an X-ray diffraction method is smaller than 55.degree.,
and a number of free fibrils is 50/1000 d/0.1 mm or 25/1000 d/0.1
mm, or the like. This three-dimensional plexifilamentary fiber has
a non-circular cross section, and a large specific surface area, an
excellent light scattering property, a superior bulkiness, and a
high strength. Therefore, it is possible to make a nonwoven fabric
having a high covering property and a high strength by utilizing
the shape and characteristics of this fiber.
After much research, the inventors of the present application have
succeeded in the development of a polypropylene three-dimensional
plexifilamentary fiber having novel characteristics. The features
of this polypropylene plexifilamentary fiber are that this fiber
has a microwave birefringence of 0.07 or more, a superior
dimensional stability in a heated environment, and a high tensile
strength, a high fiber spreadability or the like. In particular,
between 0.1 wt % and 10 wt % of a spreading agent is added to this
polypropylene plexifilamentary fiber to apply a high fiber
spreadability to the fiber, and a nucleating agent, a lubricant or
a crystalline resin except a base resin, can be used in this fiber
as the spreading agent. This fiber is disclosed in Japanese
Unexamined Patent Publications (Kokai) No. 1-104814 and No.
1-132819, and the corresponding PCT application filed as PCT/JP
87-00808.
Known methods of manufacturing a polypropylene three-dimensional
plexifilamentary fiber will be described hereafter.
These methods have been disclosed in U.S. Pat. No. 3,467,744, U.S.
Pat. No. 3,564,088, U.S. Pat. No. 3,756,441 corresponding to
Japanese Unexamined Patent Publication (Kokai) No. 49-42917, and
Japanese Unexamined Patent Publication (Kokai) No. 62-33816 filed
by the same applicant as that of the present application.
In the above known publications, a dope having an isotactic
polypropylene content of between 2 wt % and 20 wt % is prepared by
using a solvent, such as a 1,1,2-trichloro-1,2,2-trifluoroethane, a
trichloro fluoromethane or the like, a uniform dope is made from
the above dope under a pressure of a two-liquid-phase boundary
pressure or more, and the uniform dope is extruded through a
pressure let-down zone having a pressure of a two-liquid-phase
boundary pressure or less, into an environment of an atmospheric
pressure to thereby obtain a fiber. In these processes, the type of
solvent, concentration of the isotactic polypropylene, MFR of the
isotactic polypropylene, a temperature and a pressure of a solution
prepared from the solvent and the isotactic polypropylene, a
relationship between MFR, a concentration of the polypropylene and
a temperature of the solution during an extruding operation, or the
like have been suitably selected. In Japanese Unexamined Patent
Publication (Kokai) No. 62-33816, the diameter of a nozzle is
specified.
In a method of manufacturing a polypropylene three-dimensional
plexifilamentary fiber disclosed in Japanese Unexamined Patent
Publications (Kokai) No. 1-104814 and No. 1-132819, and the
corresponding PCT application of PCT/JP87-00808, filed by the same
inventors as those in the present application, a specific
temperature and pressure of the solution were selected and a dope
having a high viscosity was used. In particular, when manufacturing
a highly spread plexifilamentary fiber, a spreading agent was added
to the dope, the dope with the spreading agent was spun and then
subjected to a spreading operation.
Several problems arising in the conventional polypropylene
three-dimensional plexifilamentary fiber will be described
hereafter.
A serious problem arising with the conventional known polypropylene
three-dimensional plexifilamentary fiber is that the fiber
spreadability is poor, and accordingly, it is impossible to make a
nonwoven fabric having superior characteristics from the known
polypropylene three-dimensional plexifilamentary fiber. With regard
to the above, the polypropylene is inferior to a high-density
polyethylene known to date.
The term "fiber spreadability" in the present specification means
that a fiber extruded from a spinneret having a hole is separated
into finer units e.g., each fibril constituting a plexifilamentary
fiber.
A fiber spreading degree expressing a quality of the fiber
spreadability can be evaluated by a number of free-fibrils and a
fiber width thereof. The number of free-fibrils is a measure
expressing a degree by which the fiber is spread to the finer unit
and is shown as a number of separated fibrils per unit weight of
the fiber. A larger value of the number of free-fibrils shows that
the fiber is more finely separated.
The fiber width is a extent in a direction perpendicular to an axis
of the fiber observed when a fiber extruded from the single hole of
the spinneret is widen in a two-dimensional state in both an axial
direction of the fiber and a direction perpendicular to the axial
direction of the fiber. Since the fiber width depends on a quantity
of the fiber used for measuring the fiber width, the fiber width is
expressed as a value per unit quantity of the fiber, e.g., 10
mm/100 d. When the fiber is uniformly spread in a widthwise
direction of the fiber, it is possible to approximately evaluate
the fiber spreading degree only from the fiber width.
It is usually necessary for the fiber width to be 20 mm/100 d or
more, to obtain a nonwoven fabric having a light weight per unit
area and a high uniformity by piling a plurality of spread fibers,
preferably 30 mm/100 d or more.
Nevertheless, even if the conventional known conventional
polypropylene plexifilamentary fibers are spread by using an
impingement plate, the obtained fiber width of the fiber is 10
mm/100 d at most.
Another problem of the known conventional polypropylene
plexifilamentary fiber is that a strength of the fiber is lower.
For example, Japanese Examined Patent Publication (Kokoku) No.
42-19520 disclosed a method of spreading a fiber stream extruded
from a spinneret, by arranging an impingement plate in such a
manner that the fiber stream is impinged on the impingement plate.
A tensile strength of the fiber shown in an Example 9 in this
publication is only 0.53 g/d, which is too low as a value of the
fibers used in the nonwoven fabric.
As described herebefore, it has been difficult to obtain a
plexifilamentary fiber having a high tensile strength and a large
fiber width by using a polypropylene polymer, and although an
improvement in which a nozzle of the spinneret is provided with a
rectangular groove has been proposed, to solve the above problems,
as disclosed in U.S. Pat. No. 3,467,744, U.S. Pat. No. 3,564,088
and Japanese Unexamined Patent Publication (Kokai) No. 49-42917,
and a plexifilamentary fiber having a large fiber width can be
obtained by this improvement, a tensile strength of the obtained
fiber is still too low. Further, it is difficult to apply a
dispersing and piling operation required when manufacturing a
nonwoven fabric, which is a main application of a flash spun
fiber.
Another problem of the conventional known polypropylene
three-dimensional plexifilamentary fiber is that a thermal
stability thereof is poor, that is, a dimensional stability under a
heated atmosphere is poor, resulting in a large elongation and an
easy deformation in a heated atmosphere.
As described herebefore, the same inventors as those of the present
invention proposed the polypropylene three-dimensional
plexifilamentary fiber having an improved tensile strength and
thermal stability, and a superior fiber spreadability, and
manufactured by adding a spreading agent, in Japanese Unexamined
Patent Publications (Kokai) No. 1-104814 and No. 1-132819, and the
corresponding PCT application No. PCT/JP87-00808. Nevertheless, the
inventors found that a problem arose due to the use of the
spreading agent, after filing the applications relating to the
above fiber and a method of manufacturing the fiber. Namely, a
clogging in a filter of a spinning apparatus is generated by the
spreading agent which is little solved in a solvent under a high
temperature and a high pressure, such as a benzoate, an inorganic
powder, a polyamide resin or the like, and further, the nozzles of
the spinneret are clogged, resulting in an obstruction of a staple
spinning of the fiber.
Recently, problems regarding a solvent used for spinning a
polypropylene three-dimensional plexifilamentary fiber has arisen.
Namely, restriction of a production and consumption of a specified
chlorinated hydrocarbon or a specified brominated hydrocarbon in
which all of the hydrogen is substituted by a halogen, was
started.
As the solvent used for manufacturing a polypropylene
three-dimensional plexifilamentary fiber, U.S. Pat. No. 3,467,744
and U.S. Pat. No. 3,568,088 disclosed a
1,1,2-trichloro-1,2,2-trifluoroethane, and U.S. Pat. No. 3,568,088,
U.S. Pat. No. 3,756,441, Japanese Unexamined Patent Publications
(Kokai) No. 1-104814 and No. 1-111009 disclosed a
trichlorofluoromethane.
When a nonwoven fabric, which is a main application of a flush spun
fiber, is manufactured from the polypropylene three-dimensional
plexifilamentary fiber by accumulating spread fibers to make a web,
the spread fibers are usually electrostatically charged by a corona
discharge, as disclosed in U.S. Pat. No. 3,456,156. In this case,
when a combustible solvent is used, there is a risk of an ignition
or an explosion of the solvent. Accordingly, a nonflammable solvent
must be used for this purpose. The nonflammable solvent is
generally selected from a chlorinated hydrocarbon, a fluorinated
hydrocarbon, a chlorinated and fluorinated hydrocarbon. In
practice, a trichlorofluoromethane,
1,1,2-trichloro-1,2,2-trifluoroethane, a dichloromethane, and a
mixture of the above solvents or the like, are preferably used.
Further, to protect the ozone layer, the Vienna Treaty was adopted
on 1985, followed by the Montreal Protocol in which the content of
Vienna Treaty is concretely determined. Accordingly, a law stemming
from the Vienna Treaty and Montreal Protocol was established in
Japan, and a control based on the above law started from July,
1989. Namely, a production and a consumption of a specified
material, having an especially large influence on the depletion of
the ozone layer in various specified chlorinated or brominated
hydrocarbons in which all of the hydrogen is substituted by the
halogen and having a superior stability in the atmosphere and a
large ozone layer depletion potential have been controlled.
The above-described trichlorofluoroethane and
1,1,2-trichloro-1,2,2-trifluoroethane were fall under this control,
and the production and consumption of the specified chlorinated or
brominated hydrocarbons in which all of the hydrogen is substituted
by the halogen may be completely stopped by the year 2000.
From the above-described situation, the use of a chlorinated and
fluorinated hydrocarbon in which all the hydrogen is substituted by
a chlorine and a fluorine, having a superior stability in the
atmosphere and broadly used as a preferable solvent for
manufacturing the polypropylene three-dimensional plexifilamentary
fiber, becomes difficult. Accordingly, a solvent having suitable
characteristics for manufacturing the polypropylene
three-dimensional plexifilamentary fiber and having a lower ozone
layer depletion potential is now required.
SUMMARY OF THE INVENTION
The present invention aims to provide a novel polypropylene
three-dimensional plexifilamentary fiber free of a spreading agent
and having a high fiber spreadability, a high thermal dimensional
stability, and a superior processability.
A second object of the present invention is to provide a novel dope
capable of stably manufacturing the polypropylene three-dimensional
plexifilamentary fiber free of a spreading agent and having a high
fiber spreadability, a high thermal dimensional stability and a
superior processability, and preferably in which a substance having
a lower ozone layer depletion potential is used as a solvent in the
dope.
A third object of the present invention is to provide a novel
method of manufacturing the polypropylene three-dimensional
plexifilamentary fiber in accordance with the present
invention.
The primary object of the present invention is attained by a
polypropylene fibrillated three-dimensional plexifilamentary fiber
characterized in that the fiber has a microwave birefringence of
0.07 or more and Mw/Mn of 4.3 or less, wherein Mw stands for a
weight-average molecular weight and Mn stands for a number-average
molecular weight.
The second object of the present invention is attained by a dope
from which a fibrillated three-dimensional plexifilamentary fiber
of an isotactic polypropylene is spun, characterized in that the
dope is composed of an isotactic polypropylene having Mw/Mn of 4.3
or less and MFR of 20 or less, and a halogenated hydrocarbon used
as a solvent of the isotactic polypropylene. To prevent the
depletion of the ozone layer, it is preferable to use a
2,2-dichloro-1,1,1-trifluoroethane or a
1,2-dichloro-trifluoroethane as the halogenated hydrocarbon.
The third object of the present invention is attained by a method
of manufacturing a fibrillated isotactic polypropylene obtained by
passing a dope composed of an isotactic polypropylene and a
halogenated hydrocarbon through a pressure let-down chamber and a
spinneret, and extruding the dope into a lower temperature and
lower pressure zone, characterized in that a dope composed of an
isotactic polypropylene having Mw/Mn of 4.3 or less and MFR of 20
or less and a halogenated hydrocarbon used as a solvent of the
isotactic polypropylene is used.
BRIEF EXPLANATION OF THE DRAWINGS
FIG. 1 is a graph explaining a relationship between a
weight-average molecular weight Mw and a tensile strength in
various fibers manufactured by using isotactic polypropylene raw
materials having different values of a weight-average molecular
weight per a number-average molecular weight;
FIG. 2 is a graph illustrating cloud point curves of dopes in
accordance with the present invention and composed of a
polypropylene and various halogenated hydrocarbons; and
FIG. 3 is a graph illustrating a cloud point curves of dopes in
accordance with the present invention and composed of a
polypropylene and a blended halogenated hydrocarbon.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in detail hereinafter with
reference to the accompanying drawings, which are used for
explaining a polypropylene three-dimensional plexifilamentary
fiber, and a dope used for manufacturing the fiber in accordance
with the present invention.
First, a polypropylene fibrillated three-dimensional
plexifilamentary fiber in accordance with the present invention
will be described.
The feature of the fiber in accordance with the present invention
is that the fiber has a microwave birefringence of 0.07 or more and
Mw/Mn of 4.3 or less, and this fiber is free of a spreading
agent.
When the microwave birefringence of the obtained fiber is 0.07 or
more and the Mw/Mn of the obtained fiber is 4.3 or less, a fiber
having the same fiber spreadability or more compared with a
polypropylene three-dimensional plexifilamentary fiber including a
spreading agent can be obtained. Accordingly, it becomes
unnecessary to add the spreading agent to the fiber and a dope used
for manufacturing the fiber by the present invention.
There is a tendency for a lower value of Mw/Mn of the fiber to be
used, and a higher fiber spreadability is obtained. Accordingly it
is preferable to adopt an Mw/Mn of 3.8 or less.
Further, preferably a melt flow rate (hereafter, referred to as
MFR) of a polymer constituting the fiber is between 2 and 20. When
the polymer having an MFR of 20 or more is used, it is difficult to
obtain a fiber having a high tensile strength, and when the polymer
having a lower MFR value is used, the tensile strength becomes
higher. When the polymer having an MFR of 2 or less is used, a
fibrillation of the fiber is not sufficient, resulting in a lower
tensile strength. More preferably, the MFR is between 3.5 and
10.
The value of the MFR of the polymer corresponds generally to a
weight average molecular weight of the polymer. Accordingly, a
preferable range of the polymer. Accordingly, a preferable range of
the weight-average molecular weight of the polypropylene
three-dimensional plexifilamentary fiber is approximately between
15.times.10.sup.4 and 28.times.10.sup.4, more preferably
approximately between 18.times.10.sup.4 and 25.times.10.sup.4.
In the polypropylene three-dimensional plexifilamentary fiber
satisfying the microwave birefringence of 0.07 or more, Mw/Mn of
4.3 or less and MFR of between 2 and 20, a tensile strength of the
fiber is approximately 2 g/d, and an elongation under heat is about
8% or less at 100.degree. C. and about 12% or less at 130.degree.
C. When the fiber has a microwave birefringence of 0.10 or more, a
tensile strength of the fiber is about 3.5 g/d or more, and an
elongation under heat is about 4% or less at 100.degree. C. and
about 6% or less at 130.degree. C. Further, if the value of the
Mw/Mn of the fiber becomes to a small, the tensile strength of the
fiber becomes to a high.
In the fiber in accordance with the present invention, the
microwave birefringence effects mainly an improvement of a thermal
dimensional stability and the Mw/Mn effects mainly an improvement
of a fiber spreadability and a tensile strength of the fiber.
However, each factor effects the improvements of each
characteristic with a mutually affected relationships, and the
polypropylene three-dimensional plexifilamentary fiber having
superior characteristics in accordance with the present invention
can be obtained by simultaneously only by satisfying the desirable
values of the microwave birefringence and Mw/Mn.
The polypropylene three-dimensional plexifilamentary fiber in
accordance with the present invention has essentially a superior
fiber spreadability as described above, and accordingly, when the
obtained fiber is subjected to a spreading operation well known in
this technical field, a spread fiber having a number of free
fibrils of 100/50 d or more and a fiber width of 20 mm/100 d or
more can be obtained, and a nonwoven fabric having a high utility
can be obtained by piling the obtained spread fibers to make a web,
and heat-bonding the web.
A definition and a method of measuring technical terms expressing
the characteristics of the fiber in accordance with the present
invention will be described hereafter.
A microwave birefringence (.DELTA.n) is meant the difference
(.DELTA.n=n.sub.MD -n.sub.TD) between the refractive index
(n.sub.MD) in the direction of the fiber axis and the refractive
index (n.sub.TD) in the direction perpendicular to the fiber axis,
determined by electromagnetic waves of the microwave region (the
frequency range of from 0.3 GHz to 30 GHz). The orientation of the
molecule, that is the orientation of the crystalline region and the
amorphous region can be evaluated based on the microwave
birefringence as well as the birefringence determined by the
so-called optical measurement method using visible waves. For the
fiber of the present invention having a non-circular cross-section,
the measurement is difficult by the customary measurement method
using a polarization microscope because the fibril thickness
greatly differs and the method using microwaves is effective.
The microwave birefringence is measured at a frequency of 4.0 GHz
by a microwave molecule orientation meter (Model MOA-2001A supplied
by Kanzaki Seishi K.K.). Specimens used for the measurement are
prepared by arranging the fiber in the parallel state in holders
such that a width of the fiber is 10 mm, a necessary length is 75
mm and a substantial thickness is about 100 .mu.m. The substantial
thickness, which is necessary for calculating the microwave
birefringence, is calculated from a number of fibers, a fineness
and density of the fibers.
In Mw/Mn, Mw stands for a weight-average molecular weight and Mn
stands for a number-average molecular weight, as described before.
The weight-average molecular weight and the number-average
molecular weight are measured at the temperature of 135.degree. C.
by gas chromatography (Model 150-CGPC supplied by Waters Co.,
Ltd.). In this measurement, trichlorobenzene is used as a solvent.
Since a monodispersed standard specimen of a polypropylene is
difficult to obtain, a conversion value used for a polyethylene is
used. Namely, a molecular weight conversion factor obtained from a
relationship between a standard specimen of a polystyrene and a
standard specimen of a polyethylene is used.
The thermal dimensional stability can be evaluated by an elongation
under heating of the fiber, the elongation under heating is
measured at the heat-up rate of 5.degree. C./min and at the
temperature between 30.degree. C. and 170.degree. C., by a thermal
mechanical analysis apparatus (Model TMA-40 supplied by Shimazu
Seisakusho K.K.). In the measurement, a fineness of a sample is
measured, a load of 0.1 g/d, i.e., a load of about 810 gf/mm.sup.2,
is applied to an end of the sample, and the sample is held between
two chucks separated by about 2 mm to 4 mm. When a spread fiber is
measured, the sample is measured after a twist of 8 turns per cm is
applied.
The tensile strength and elongation of the fiber are measured at a
pulling speed of 200 mm/min, by an Instron tensile tester, with
respect to a sample twisted at 8 turns per cm.
The measurement of the fineness and the twist operation of the
fiber are performed on a sample applied with an initial load of 0.6
g/d, except where a breakage occurs or a drawing of the fiber is
generated, because there is no probability that the drawing of the
fiber will be generated under the load of 0.6 g/d. In particular,
it is necessary to use the initial load of 0.6 g/d when a spread
fiber of an isotactic polypropylene is measured, because this
spread fiber has a high elasticity. Accordingly, if a smaller
initial load than 0.6 g/d is used, the measurement of fineness and
the twist operation are performed for the spread fiber holding
flexed fibrils applied by spreading operation, and thus an
erroneous measurement is obtained. When the breakage of the fiber
is generated under the initial load of 0.6 g/d, the initial load is
lowered to a value at which the fiber will not break.
The number of free fibrils is measured by counting the number of
separated fibrils, by using a microscope with an object lens of 1.6
magnifications and an eyepiece of 10 magnifications, and moving a
visual field in the transverse direction of the fiber.
The fiber width is obtained by peeling a spread fiber from a
slightly pressed web formed by piling the spread fibers and
measuring a fiber width perpendicular to an axis of the spread
fiber. When the web is not formed, the fiber width is measured by
receiving the fiber in the spread state after the spreading
operation on a net of a coarse mesh size (about 10 mesh).
A dope from which a polypropylene fibrillated three-dimensional
plexifilamentary fiber of an isotactic polypropylene is spun will
be described hereafter.
It is necessary to improve characteristic of the dope from which
the polypropylene fibrillated three-dimensional plexifilamentary
fiber is spun, to manufacture the fiber in accordance with the
first invention in this application free from a spreading
agent.
Namely, the second object of the present invention is attained by a
dope composed of an isotactic polypropylene having an Mw/Mn of 4.3
or less and an MFR of 20 or less, and a halogenated hydrocarbon
used as a solvent of the isotactic polypropylene.
The Mw/Mn and MFR of the isotactic polypropylene in the dope cannot
be measured. Accordingly, it is assumed that the values of the
Mw/Mn and MFR of the isotactic polypropylene in the dope are
substantially identical to those of the fiber extruded from a
spinneret, and the Mw/Mn and MFR of the fiber are measured and used
as Mw/Mn and MFR of the isotactic polypropylene in the dope.
When the isotactic polypropylene in the dope having an Mw/Mn of 4.3
or less and an MFR of 20 or less is used, a polypropylene
three-dimensional flexifilamentary fiber having a high fiber
spreadability in accordance with the present invention can be
stably manufactured. It is preferable to use the isotactic
polypropylene in the dope having an MFR of 2 or more and a smaller
Mw/Mn. When the isotactic polypropylene in the dope has an Mw/Mn of
4.3 or more, the fiber spreading degree of the obtained fiber
becomes lower and a pressure in a pressure let-down chamber of a
spinning apparatus fluctuates. Accordingly, it is impossible to
obtain a stable spinning operation. More preferably, the Mw/Mn is
3.8 or less and the MFR is 10 or less.
To obtain the second object of the present invention, preferably
the dope is prepared by using an isotactic polypropylene having an
Mw/Mn of 4.8 or less and an MFR of 7 or less, as a polymer of a raw
material. This condition must be applied for a process in which a
melting operation of the isotactic polypropylene and an preparation
of a solution composed of the isotactic polypropylene and a
solvent, using an apparatus in which a retention time of the
isotactic polypropylene and the solution in a spinning apparatus is
short e.g., an extruder. When the isotactic polypropylene used as
the polymer of the raw material has an Mw/Mn of 4.8 or less and an
MFR of 7 or less, even if the retention time of the isotactic
polypropylene is short, such as within 2 minutes, a fiber having a
high fiber spreadability can be stably manufactured.
When the dope is prepared by using an apparatus in which the
retention time of the isotactic polypropylene and the solution in
the spinning apparatus is relatively long, e.g., an autoclave, the
above condition is not always necessary. But the conditions
required for the characteristics of the dope must be also satisfied
in this latter case, to manufacture a fiber having good
characteristics, in a stable spinning operation.
It is important to use a halogenated hydrocarbon group as a
solvent. These solvents have high solving power and are mostly
nonflammable. Accordingly, it is possible to solve the isotactic
polypropylene at a high temperature, e.g., 215.degree. C., and high
pressure, e.g., 200 kg/cm.sup.2 G, to prepare the dope by using the
halogenated hydrocarbon.
FIG. 1 shows a relationship between a weight average molecular
weight Mw and a tensile strength in various fibers manufactured by
using isotactic polypropylene raw materials having different Mw/Mn
values. In FIG. 1, the effects of examples 1 to 3 and comparative
examples 1 and 2, as described in detail hereinafter, are plotted.
As shown in FIG. 1, the tensile strength of the fiber depends on
the weight-average molecular weight Mw of the fiber, i.e., the
higher the Mw of the fiber, is the higher the tensile strength of
the fiber. Nevertheless, the tensile strength of the fiber depends
more strongly on the Mw/Mn of the isotactic polypropylene used as
the raw material. Namely, when the fiber is spun from a dope
prepared by using an isotactic polypropylene having an Mw/Mn of 4.8
or less and an MFR of 7 or less, the tensile strength of the fiber
becomes higher.
It is essential in the present invention that the MFR of the
isotactic polypropylene be 7 or less. When the isotactic
polypropylene used as the raw material has an Mw/Mn of 4.8 or more
and an MFR of 7 or less, the microwave birefringence of the fiber
satisfies the condition of 0.07 or more, and a polypropylene
three-dimensional flexifilamentary fiber having a high tensile
strength and a high thermal dimensional stability can be obtained.
When the MFR is larger than 7, the thermal dimensional stability of
the fiber is often lowered and the tensile strength thereof becomes
poor.
The MFR is measured at a temperature of 230.degree. C. under a load
of 2.16 kg, by using a melt indexer supplied by Toyo Seiki
Seisakusho according to JIS K-7210.
It is difficult to commercially obtain an isotactic polypropylene
having an Mw/Mn of 4.8 or less but a molecular weight of a
relatively large value, and having an MFR of 7 or less, and
accordingly, it is important to adjust a market grade polypropylene
polymer to form a polypropylene polymer satisfying the
above-described conditions. Namely, a polypropylene polymer to be
used for a dope and having an MFR of 7 or less, preferably 3.5 or
less and an Mw/Mn of 4.8 or less, preferably 4.5 or less is made by
degradating a raw material of the polypropylene having a relatively
large molecular weight, e.g., an MFR of 1.5 or less and an Mw/Mn of
4.8 or more.
It is possible to use the following two methods to degradate the
polypropylene. The first method is a degradating method using heat,
and the second method is a degradating method using a decomposer
such as an organic peroxide or the like.
The first method is carried out by processing a polymer through an
extruder in which the polymer is melted, and the second method is
carried out by mixing a decomposer such as organic peroxide with a
polymer chip and processing the polymer with the decomposer in the
extruder.
The MFR of the raw material degradated by heat lies within a
relatively broad range and has a larger variance. Further, although
a relatively lower degradation of the polymer can be only attained
by heating, in the degradation using the decomposer, a degree of
degradating of the polymer is directly determined by a quantity of
the decomposer used. Accordingly it is possible to control the MFR
of the degradated polymer on the basis of the quantity of the
decomposer used. Further, a range of the MFR of the degradated
polymer is narrow and a variance of the MFR is a small. Even if the
decomposer remains in the polymer, the remaining decomposer will
not have an undesirable effect on the subsequent process.
Therefore, the degradating by the decomposer is preferable to the
degradating by heat.
It is preferable to use a 1,3-bis(t-butylperoxiisopropyl)benzene, a
2,5-dimethyl 2,5-di-(t-butylperoxi)hexane or dialkylperoxide such
as 2,5-dimethyl-2,5-di(t-butylperoxi)hexyne-3 or the like as the
decomposer. When the MFR of the raw material is degradated from 0.5
to a value of between 2.0 and 3.0, by using the
1,3-bis(t-butylperoxiisopropyl)benzene as the decomposer, between
100 ppm and 160 ppm of the decomposer may be added to the raw
material.
A single screw extruder may be used to uniformly degradate the
polymer. Further preferably a mixing portion such as a dulmage type
mixing portion is provided on the extruder.
Usually, a raw material degradated as described before may be
stocked and supplied to a flash spinning process, but the polymer
can be degradated just before the polymer solution is prepared from
the polymer and the solvent. Namely, in the flash spinning process
in which the polymer of a raw material is melted by an extruder and
is supplied to a solution preparing portion, the degradating
process may be performed before the molten polymer is mixed with a
solvent.
When the dope in accordance with the present invention is prepared,
it is possible to prevent a depletion of the ozone layer by using a
2,2-dichloro-1,1,1-trifluoroethane or a
1,2-dichloro-trifluoroethane as a halogenated hydrocarbon.
FIG. 2 shows examples of phase charts of dopes composed of an
isotactic polypropylene and a 2,2-dichloro-1,1,1-trifluoroethane or
a 1,2-dichloro-trifluoroethane. In FIG. 2, cloud points show the
generation of a phase separation. .DELTA.n observation of the cloud
point is performed by an autoclave with two viewing windows through
which light can pass. An extinction initiation point and an
extinction termination point can be observed for the dope including
the polypropylene. In FIG. 2, the cloud points are expressed by the
extinction termination points. As can be seen from FIG. 2, the
cloud points of the two above halogenated hydrocarbons are biased
toward a lower temperature and a higher pressure than those using a
conventional solvent for the polypropylene, i.e., a
trichlorofluoromethane.
The most important feature when using either of the two above
halogenated hydrocarbons is that a volume of the solution extruded
from a spinneret is larger. For example, the volume of the solution
in this case is about two times that in which a
trichlorofluoromethane is used as a solvent. Even if a spinneret
having a hole of the same diameter is used, the productivity of a
fiber when using either one of the above two halogenated
hydrocarbons is about two times greater than that of the latter
case. It appears that the increase of the productivity obtained by
using either one of the above two halogenated hydrocarbons is
because a suitable pressure in a pressure let-down chamber is a
higher pressure and critical pressure is lower pressure.
With regard to protection of the ozone layer, an ozone depletion
potential is calculated at 0.02 for the
2,2-dichloro-1,1,1-trifluoroethane and it appears that the ozone
depletion potential of the 1,2-dichloro-trifluoroethane has the
same level as that of 2,2-dichloro-1,1,1-trifluoroethane, but the
ozone depletion potential of a trichlorofluoromethane is calculated
as 1.00. Accordingly, the above two halogenated hydrocarbons are
suitable for preventing the depletion of the ozone layer.
When the 2,2-dichloro-1,1,1-trifluoroethane or the
1,2-dichloro-trifluoroethane is used as the halogenated
hydrocarbon, a dichloromethane is preferably added to either one of
the above two halogenated hydrocarbon, by 80 wt % of the total
weight of the solvent. The blended solvent has the same solubility
as that of a solvent constituted with the same component. FIG. 3
shows a curve of an extinction termination point when a solvent
blended with a dichloromethane of 50 wt % and
2,2-dichloro-1,1,1-trifluoromethane of 50 wt % is used, and cloud
points are clearly observed.
As can be seen when comparing FIG. 3 with FIG. 2, each cloud point
moves toward a higher temperature side and a lower pressure side.
Further, a range of moving of the cloud point depends on a weight
of the dichloromethane added to the solvent. Accordingly, it is
possible to spin the fiber under the same temperature and pressure
as when a conventional trichlorofluoromethane is used, by changing
a blending weight of the dichloromethane. For example, when
preparing a dope including 10 wt % of the isotactic polypropylene
having an Mw/Mn of 4.0 and an MFR of 6 by using a solvent blended
with the 2,2-dichloro-1,1,1-trifluoroethane of 20 wt % and the
dichloromethane of 80 wt %, the isotactic polypropylene can be
dissolved at the temperature of 215.degree. C. and a pressure of
between 70 kg/cm.sup.2 G and 165 kg/cm.sup.2 G. When the
dichloromethane is over 80 wt % in the solvent, the spreadability
of the obtained fiber becomes lower, it is necessary to make a
suitable spinning temperature higher to have the spread ability,
and this causes a retrogradation of the polypropylene. Then, the
strength of the obtained fiber becomes weak.
Since the ozone layer depletion potential of the dichloromethane is
extremely weak, the above blended solvent is useful for the
prevention of the depletion of the ozone layer.
A method of manufacturing the polypropylene three-dimensional
plexifilamentary fiber in accordance with the present invention
will be described hereafter.
As described herebefore, in a method of manufacturing a fibrillated
three-dimensional plexifilamentary fiber of an isotactic
polypropylene obtained by passing a dope composed of an isotactic
polypropylene and a halogenated hydrocarbon through a pressure
let-down chamber and a spinneret, and extruding the dope into a
lower temperature and lower pressure zone, the third object of the
present invention can be attained by a method characterized in that
a dope composed of an isotactic polypropylene having an Mw/Mn of
4.3 or less and an MFR of 20 or less, and a halogenated hydrocarbon
used as a solvent of the isotactic polypropylene, is used.
In the above manufacturing method, preferably a dope prepared by
using an isotactic polypropylene having Mw/Mn of 4.8 or less and
MFR of 7 or less as a polymer of a raw material is used, and it is
preferable to use 2,2-dichloro-1,1,1-trifluoroethane or
1,2-dichloro-trifluoroethane as the halogenated hydrocarbon.
Further, it is preferable to use a solvent including a
dichloromethane having a content of 80 wt % or less in the solvent
and another halogenated hydrocarbon.
A concentration of the isotactic polypropylene in the solution may
be between 5 wt % and 20 wt %. When the concentration of the
isotactic polypropylene in the solution is below 5 wt %, it is
difficult to obtain a fiber having a suitable microwave
birefringence value and a tensile strength of the obtained fiber
becomes poor. The higher the concentration of the isotactic
polypropylene, the higher the tensile strength of the fiber.
Therefore, the preferable value of the concentration is 8 wt % or
more. Nevertheless when a solution in which the concentration of
the isotactic polypropylene is over 20 wt % is used, the
flowability of the solution drops, and a flashing power thereof is
weakened, which results in an inferior fiber spreadability of the
obtained fiber. Further it is impossible to obtain a highly spread
fiber constituted with a plurality of fine fibrils.
A conventional known method can be used as a flash spinning
technique. Namely, the flash spinning of the fiber in accordance
with the present invention can be attained by keeping a solution in
which the isotactic polypropylene is dissolved with the halogenated
hydrocarbon such as the 2,2-dichloro-1,1,1-trifluoroethane or the
like under a high temperature and a high pressure, reducing a
pressure of the solution in a pressure let-down chamber to lower
the pressure thereof to a pressure below a phase separating point,
and extruding the solution through a spinneret into a zone having a
low temperature and a low pressure. It is preferable to use a
method in which a solution flow extruded from the spinneret is
impinged onto an impingement plate as a fiber spreading
operation.
Suitable conditions for the flash spinning method will be described
hereafter.
A desirable flash spinning may be performed by a flash spinning
apparatus in which a screw type extruder, a solvent introducing
zone, a mixing zone, a pressure let-down chamber, and a spinneret
are consecutively arranged. First, the isotactic polypropylene
having the specific characteristics described herebefore as the raw
material is supplied into and melted in the screw type extruder,
and the molten isotactic polypropylene is blended with the
halogenated hydrocarbon supplied from the solvent introducing zone
in the mixing zone to make a homogeneous solution. It is important
to keep the pressure of the solution in the position upstream of
the pressure let-down chamber at a pressure higher than the
pressure in the corresponding extinction initiation point of the
solution used, to stably spin the fiber, but it is possible to use
a condition exceeding the pressure and the temperature in the
corresponding extinction termination point of the solution used, at
a position just upstream of the pressure let-down chamber. Namely,
in this position, if the temperature used is the same as that in
the extinction termination point, the pressure shifted from the
pressure of the extinction termination point toward a higher
pressure may be adopted, and if the pressure used is the same as
that in the extinction termination point, the temperature shifted
from the temperature of the extinction termination point toward a
lower temperature may be adopted.
An orifice may be provided between the mixing zone under the high
pressure and the pressure let-down chamber, and a temperature in
the pressure let-down chamber is preferably between 198.degree. C.
and 220.degree. C. When the temperature is under 198.degree. C., it
is impossible to increase a flow volume of the solution, which
results in a lower flowability and a weaker flashing power.
Therefore, the obtained fiber extruded from the spinneret has a
lower orientation and it is difficult to spin a fiber having a high
microwave birefringence. When the temperature is over 220.degree.
C., an adhering between fibrils and retrogradation of the
polypropylene is likely to be generated.
It is preferable to use a pressure below the pressure in the
corresponding extinction termination point of the solution used as
in the pressure of the pressure let-down chamber. If a pressure
higher than the pressure in the corresponding extinction
termination point is used in the pressure let-down chamber, the
obtained fiber has a fiber configuration in which particle-like
materials appear because the fiber is not fibrillated, which
results in a fiber having a high elongation and a low tensile
strength, and an elongation under heating of the fiber becomes
higher. If a pressure below a vapor pressure of the halogenated
hydrocarbon is used in the pressure let-down chamber, breakage of
the fibrils is generated, which results in a lower microwave
birefringence and a higher elongation under heating.
In the present invention, the isotactic polypropylene used
comprises about 85 wt % or more of the isotactic polypropylene, and
another polymer component such as ethylene, n-butylene,
isobutylene, vinyl acetate or methyl methacrylate can be used in an
amount of up to about 15 wt %. Moreover, additives such as an
antioxidant, an ultraviolet absorber, a lubricant, a filler, a
nucleating agent, an antistatic agent and a colorant can be added
in amounts that will not degrade the characteristics of the
isotactic polypropylene.
When a dope satisfying claims 3 to 8 is used, the dissolution of
the isotactic polypropylene and the extrusion of the dope can be
accomplished not only by the continuous method using a screw
extruder as described herebefore but also by a batchwise method
using an autoclave or the like.
As described herebefore, the fiber in accordance with the present
invention has specific microwave birefringence value and Mw/Mn, and
further, has the following features. Namely the orientation angle
of the fiber measured by X-ray diffractometry is about 36.degree.
or less, preferably 30.degree. or less. The long period of the
fiber is preferably between 75 .ANG. and 140 .ANG.. The apparent
density of the fiber is 0.895 g/cm.sup.3 or more, preferably 0.90
g/cm.sup.3 or more, and the specific surface area of the fiber is
preferably between 2 m.sup.2 /g and 30 m.sup.2 /g.
As described herebefore, the same inventors as those of the present
invention proposed a prototype of the polypropylene
three-dimensional plexifilamentary fiber, in PCT application of No.
PCT/JP87/00808. To clarify the differences between the present
invention and the invention claimed in the PCT application No.
PCT/JP87/00808, the differences in the main characteristics of both
inventions is shown in Table 1.
TABLE 1 ______________________________________ Present Invention of
Invention PCT/JP87/008 Isotactic Isotactic Polymer used
Polypropylene Polypropylene ______________________________________
Polymer used as Raw Material -- Mw/-- Mn 4.8 or less Not Defined
MFR 7 or less Not Defined Polymer in Dope -- Mw/-- Mn 4.3 or less
Not Defined MFR 20 or less Not Defined Fiber Microwave 0.07 or more
0.07 or more Birefringence -- Mw/-- Mn 4.3 or less Not Defined
Spreading Agent Not used Used Solvent preferable
2,2-dichloro-1,1,1- Trichloro- solvent trifluoroethane
fluoromethane 1,2-dichlorotrifluoro- ethane Blended solvent in-
cluding dichloromethane of 80 wt % or less and either one of the
above two solvents ______________________________________
The features of the polypropylene three-dimensional
plexifilamentary fiber, the dope used for manufacturing the fiber,
and the method of manufacturing the fiber will be described
hereafter.
The polypropylene three-dimensional plexifilamentary fiber in
accordance with the present invention has a superior fiber
spreadability, and accordingly, it is possible to manufacture a
nonwoven fabric having a high uniformity in the thickness and
appearance thereof. Further, the fiber having an MFR value
satisfying a factor defined in the claim has a superior thermal
dimensional stability and a high tensile strength, and thus it is
possible to manufacture a nonwoven fabric having a superior
dimensional stability and high tensile strength in a heated
atmosphere.
The polypropylene three-dimensional plexifilamentary fiber in
accordance with the present invention can be stably manufactured by
using the novel dope in accordance with the present invention.
Since it is unnecessary to include a spreading agent in the dope,
clogging of a filter and nozzles in the spinneret is not generated,
and thus a stable spinning of the fiber is obtained.
When a dope is prepared by using the
2,2-dichloro-1,1,1-trifluoroethane or the
1,2-dichloro-trifluoroethane, and the dope is extruded from the
spinneret having a hole of the same size as that used for extruding
a dope including a conventional solvent such as a
trichlorofluoromethane, a volume extruded from the spinneret of the
dope using either of the above two solvent in accordance with the
present invention is about two times that obtained when using the
conventional solvent. Accordingly, a high productivity in the fiber
spinning process can be attained by using the dope in accordance
with the present invention.
The ozone layer depletion potential of the
2,2-dichloro-1,1,1-trifluoroethane, the 1,2-dichlorotrifluoroethane
and the dichloromethane are lower, and accordingly, the use of
these three solvents is preferable for protection of the
environment. In the present invention, it is possible to use a
solvent blended the dichloromethane with the
2,2-dichloro-1,1,1-trifluoroethane or the
1,2-dichlorotrifluoroethane, and in this case, even if there are
slight differences in a component, a molecular weight, or a
concentration of the polymer, it is possible to maintain a
temperature and a pressure used in the manufacturing process at a
constant value by suitably selecting a blending ratio of the
dichloromethane and another solvent. Accordingly it is possible to
spin the fiber in accordance with the present invention without
changing a specification of the spinning apparatus. This is
practically useful when manufacturing the fiber in accordance with
the present invention.
The polypropylene three-dimensional plexifilamentary fiber in
accordance with the present invention can be stably spun by the
manufacturing method in accordance with the present invention. When
the 2,2-dichloro-1,1,1-trifluoroethane or the
1,2-dichlorotrifluoroethane is used as a main solvent, it is
possible to increase a volume extruded from the spinneret and a
solvent having a lower ozone layer depletion potential can be used
in the manufacturing method in accordance with the present
invention. Accordingly, the manufacturing method in accordance with
the present invention is suitable for protecting the
environment.
The present invention will now be described with reference to the
following examples.
EXAMPLES 1 TO 3, AND COMPARATIVE EXAMPLES 1 AND 2
Various commercially available isotactic polypropylenes shown in
Table 2 are degradated by the two following methods, to prepare
isotactic polypropylenes able to be used as raw materials in the
manufacture of the fibers in accordance with the present invention,
and having a required MFR and Mw/Mn, respectively.
The polymer is degradated by applying a heating treatment to the
isotactic polypropylene by an extruder, or by using a decomposer.
Namely the isotactic polypropylene is supplemented with a
1,3-bis(t-butylisopropyl)benzene (Perkadox 14 supplied from Kayaku
Akzo KK), which is an organic peroxide, and then supplied to the
extruder.
The preparation of a dope and a flash spinning for manufacturing a
fiber is performed by a spinning apparatus including a polymer
solution blending and preparing zone in which an extruder having a
single screw of 30 mm.phi., a solvent introducing zone, a mixing
zone, a pressure let-down chamber and a spinneret are consecutively
arranged. Namely, the above degradated isotactic polypropylene is
supplied to the extruder to melt the polypropylene, and a
trifluoromethane is introduced into the solvent introducing zone at
a high pressure and constant pumping volume to obtain a homogeneous
dope. This dope is extruded through the pressure let-down chamber
and the spinneret, and the extruded fibers are impinged on a copper
plate inclined by 45.degree. to the extruded fibers at a position
remote from the spinneret by about 20 mm, whereby spread
three-dimensional plexifilamentary fibers are obtained.
An orifice arranged upstream of the pressure let-down chamber has a
diameter of 0.5 mm.phi. and a length of 5 mm, and an inner volume
of the pressure let-down chamber is about 3 cm.sup.3. The spinneret
in which an angle of the stream introduced from the pressure
let-down chamber to a nozzle hole is 60.degree., has nozzle having
a diameter of 0.7 mm.phi. and a length of 0.7 mm and is equipped
with a circular groove arranged coaxially to an axis of the nozzle
hole, on an outside of the nozzle hole, and having a diameter of
4.5 mm.phi. and a depth of 3.9 mm, is used. A concentration of the
polypropylene is between 8.8 wt % and 9.8 wt %, and a solution
extruding volume is between 1367 g/min and 1388 g/min. A
temperature of the solution in the mixing portion is between
202.degree. C. and 203.degree. C., and a pressure of the solution
in the mixing zone is between 228 kg/cm.sup.2 G and 272 kg/cm.sup.2
G. The above values differ slightly according to the polypropylene
used as the raw materials.
The results are shown in Table 2.
It is apparent from the values of Mw/Mn and MFR of the obtained
fiber shown in Table 2 that the Mw/Mn and MFR of the polypropylene
in the dope are included in the range defined by the present
invention.
When the Mw/Mn value of the polypropylene used as the raw material
is 4.8 or less (in this case, the MFR value is sufficiently small),
the fiber in accordance with the present invention and having a
microwave birefringence of 0.07 or more and an Mw/Mn of 4.3 or less
can be obtained from the various different grades of isotactic
polypropylenes supplied from different makers. Further, it is
apparent from Table 2 that the obtained fibers have a superior
fiber spreadability, tensile strength, and thermal dimensional
stability, respectively.
When polypropylenes having an Mw/Mn of 4.8 or more are used as the
raw materials, even if the MFR of the polypropylene has the same
value as that of the polypropylene used in the examples, the
spinning state in these cases becomes unstable, as shown in the
comparative example 2.
In the comparative example 1, the microwave birefringence of the
fiber is 0.07 or more and the MFR of the polypropylene in the dope
is 20 or less. Nevertheless, the Mw/Mn of the fiber is 4.3 or more
and the fiber spreadability of the fiber is poor.
In the comparative example 2, the microwave birefringence and the
Mw/Mn of the obtained fiber are outside the range defined by the
present invention, and thus have poor values for the fiber
spreadability, the tensile strength, and the elongation under
heating.
Note that a spread agent is not used for the examples 1 to 3 and
the comparative examples 1 and 2.
TABLE 2
__________________________________________________________________________
MFR of Polymer After Degradation Polymer And Used as Stability
Polymer Grade Before Method of Raw Material in Spinning (Supplier)
Degradation Degration a) MFR -- Mw/-- Mn Operation
__________________________________________________________________________
b) Example 1 EP-BQ 0.35 P 2.5 4.28 .smallcircle. (Mitsui-Toatsu
Kagaku) Example 2 E1000 0.50 P 2.6 4.35 .smallcircle. (Asahi Kasei)
Example 3 K1011 0.83 H 2.8 4.31 .smallcircle. (Chiso) Comparative
K1014 3.5 -- 3.5 6.02 .DELTA. Example 1 (Chiso) Comparative E1200
1.9 H 2.5 7.03 x Example 2 (Asahi Kasei)
__________________________________________________________________________
Characteristics of Fiber Tensile Strength Elongation Microwave
Number Fiber Fineness (g/d) under heating Birefrin- 3 of free Width
(Spread Before Spread c) (%) MFR -- Mw/-- Mn gence c) fibrils (mm)
Fiber) Spreading Fiber 100.degree. C. 130.degree. C.
__________________________________________________________________________
Example 1 5.1 3.94 0.116 207 31 128 4.4 3.8 3.0 4.5 Example 2 7.7
3.61 0.107 382 31 113 3.8 3.7 3.1 5.2 Example 3 8.1 3.94 0.114 309
27 117 4.3 3.8 2.6 4.3 Comparative 10.4 5.17 0.073 146 21 112 2.1
2.2 7.5 12.1 Example 1 Comparative 7.0 6.12 0.041 -- d) -- d) -- d)
0.9 -- d) 9.8 14.6 Example 2
__________________________________________________________________________
a) P: Perkadox 14 (Decomposer) used, H: Degradated by Heating b) o:
Stable, .DELTA.: Slightly Unstable, x: Unstable c) Fiber before
Applying Spreading Operation measured in Comparative Example 2,
Fibers applied with Spreading Operation measured in other Examples.
d) Measurement: Unsuccessful
EXAMPLE 4
An isotactic polypropylene (E1100 supplied by Asahi Kasei Kogyo
Kabushiki Kaisha) having MFR of 0.50 is degradated by Perkadox 14
to prepare the isotactic polypropylene able to be used as a raw
material when manufacturing the fiber in Example 4, and having an
MFR of 5.4 and an Mw/Mn of 4.46.
The preparation of a dope and the flash spinning thereof in Example
4 is performed by using the same solvent and apparatus as used in
Examples 1 to 3 and Comparative Examples 1 and 2, except that a
concentration of the polypropylene is 12%.
The results are shown in Table 3.
The MFR of the spread fiber in Example 4 is 15.3, which is within
the preferable range of the present invention. Accordingly, the
spread fiber in Example 4 has a high tensile strength and lower
elongation under heating.
TABLE 3
__________________________________________________________________________
Polymer After Degradation Characteristics of Spread Fiber And Used
Microwave Fiber Tensile Elongation Polymer as Raw Material
Birefrin- Spread- Strength Under Heating grade Decomposer MFR --
Mw/-- Mn MFR -- Mw/-- Mn gence ability a) (g/d) 100.degree. C.
__________________________________________________________________________
(%) Example 4 E1100 Peroxide 5.4 4.46 15.3 3.60 0.115 .smallcircle.
3.4 3.8
__________________________________________________________________________
a) Visual Evaluation. o: Good, .DELTA.: Slightly Inferior, x:
Inferior
EXAMPLES 5 TO 10 AND COMPARATIVE EXAMPLES 3 TO 5
Various commercially available isotactic polypropylenes shown in
Table 4 having a typical high molecular weight are degradated by
the same methods used in Examples 1 to 3, to prepare the isotactic
polypropylene able to be used as a raw material for the manufacture
of fibers, in Examples 5 to 10 and Comparative Examples 3 to 5, and
having a required MFR and Mw/Mn, respectively.
The preparation of a dope and the flash spinning in Examples 5 to
10 and Comparative Examples 3 to 5 are performed by using the same
solvent and apparatus as used in Examples 1 to 3.
The results are shown in Table 4.
When the degradated isotactic polypropylenes having an MFR of 7 or
less and an Mw/Mn of 4.8 or less are used, polypropylene
three-dimensional plexifilamentary fibers having a superior fiber
spreadability and high tensile strength are obtained. It is
apparent from Table 4 that, when the fiber has a microwave
birefringence of 0.07 or more and an Mw/Mn of 4.3 or less, a fiber
spreadability of a tensile strength of the fiber is superior.
In Comparative Example 4, the MFR of the polypropylene used as the
raw material is 7 or less, but the Mw/Mn of the polypropylene used
as the raw material is bigger than 4.8 and the Mw/Mn of the
polypropylene in the dope is bigger than 4.3. Accordingly, the
fiber in Comparative Example 3 has an inferior fiber spreadability,
small microwave birefringence, and lower tensile strength.
In Comparative Example 4, the MFR of the polypropylene used as the
raw material is 7 or less, but the Mw/Mn of the polypropylene used
as the raw material is bigger than 4.8 and the Mw/Mn of the
polypropylene in the dope is bigger than 4.3. Accordingly the fiber
in Comparative Example 4 has a microwave birefringence of 0.07 or
more, and a relatively high tensile strength, but the fiber
spreadability thereof is poor and it is impossible to manufacture a
web used for a nonwoven fabric and having a uniform thickness and a
superior appearance from this fiber, due to the inferior fiber
spreadability.
In Comparative Example 5, the MFR of the polypropylene used as the
raw material is 7 or more, and accordingly, the fiber in
Comparative Example 5 has a small microwave birefringence and lower
tensile strength.
Webs are manufactured from the fiber in Examples 5-10 by spreading
and dispersing the fiber by a rotary impingement member having
three fiber dispersing faces, piling the spread fibers on a running
net, and slightly pressing the spread fibers on the running net by
a roll. The nonwoven fabrics are manufactured by heat-bonding the
webs in Examples 5-10 by a felt calender. The obtained nonwoven
fabrics have a superior uniformity in the thickness thereof and a
high mechanical strength. For example, the nonwoven fabric
manufactured from the fibers in Example 7 and having a weight per
unit area of 60 g/m.sup.2 has the following mechanical
properties.
______________________________________ Tensile Strength Lengthwise
Direction 11.0 kg/3 cm Transverse Direction 12.2 kg/3 cm Elmendorf
Tear Strength Lengthwise Direction 0.14 kg Transverse Direction
0.15 kg ______________________________________
TABLE 4
__________________________________________________________________________
Characteristics of Fiber Polymer After Tensile Degradation and
Microwave Strength Tensile Method of Used as Raw Birefrin- Fiber
Before Strength of Polymer Degrada- Material gence of Spread-
Spreading Spread Fiber Grade tion a) MFR -- Mw/-- Mn -- Mw/-- Mn
Spread Fiber ability b) (g/d) (g/d)
__________________________________________________________________________
Example 5 K1011 P 2.63 4.65 3.72 0.082 .smallcircle. 3.0 2.5
Example 6 K1011 H 2.85 4.24 3.69 0.088 .smallcircle. 3.4 2.9
Example 7 E1100 P 2.63 4.47 4.13 0.095 .smallcircle. 3.9 3.3
Example 8 E1100 P 3.00 3.88 3.69 0.105 .smallcircle. 3.8 3.8
Example 9 E1100 P 5.46 3.71 3.37 0.113 .smallcircle. 4.1 3.8
Example 10 E1100 H 3.40 3.80 3.64 0.086 .smallcircle. 3.9 3.2
Compartive K1011 H 2.70 4.94 4.44 0.049 x 2.0 1.11 Example 3
Comparative EP-BQ H 2.54 5.34 4.86 0.074 .DELTA.-x 3.8 2.1 Example
4 Comparative K1011 p 8.10 -- -- 0.067 .smallcircle. 2.4 1.9
Example 5
__________________________________________________________________________
a) P: Perkadox 14 (Decomposer) used, H: Degraded by Heating b)
Visual Evaluation o: Good, .DELTA.: Slightly Inferior, x:
Inferior
EXAMPLES 11 AND 12
The polypropylene solutions in Examples 11 and 12 are prepared by
an autoclave. Namely, 64.1 g of an isotactic polypropylene having
an MFR of 1.3 and 546 g of a 2,2-dichloro-1,1,1-trifluoroethane (in
Example 11) or 1,2-dichloro-trifluoroethane (in Example 12) are fed
into the autoclave so that a concentration of the polypropylene
becomes 10.5 wt %. The autoclave is heated with a rotation of a
propeller type stirring machine to dissolve the polypropylene in
the solvent. The solution is further heated, and thus a pressure of
the solution is raised to completely dissolve the polypropylene.
After completing the dissolution of the polypropylene, the solution
is partially exhausted from a nozzle arranged on a bottom of the
autoclave, so that the pressure of the solution does not exceed 300
kg/cm.sup.2 G, which is a design pressure of the autoclave, and
thus the pressure of the solution is kept between 200 kg/cm.sup.2 G
and 300 kg/cm.sup.2 G. When the temperature of the solution becomes
215.degree. C., the solution is exhausted so that the pressure of
the solution is kept at a pressure lower than the pressure used in
the spinning process by 10 kg/cm.sup.2 G. When the temperature of
the solution becomes again at 215.degree. C., the stirring machine
is stopped, N.sub.2 gas is introduced from an N.sub.2 gas
introducing valve arranged on an upper portion of the autoclave, to
maintain the pressure of the solution at the predetermined value,
and simultaneously, an exhausting valve arranged on the bottom of
the autoclave is opened to exhaust the solution through a pressure
let-down orifice having a diameter of 0.65 mm and length of 5 mm,
into a pressure let-down chamber having a diameter of 8 mm and
length of 40 mm. The solution is then introduced into a spinneret
having the following specification, and extruded into the
atmosphere.
An angle of introducing the solution from the pressure let-down
chamber to
______________________________________ an nozzle hole of the
spinneret: 60.degree. Nozzle hole diameter: 0.5 mm length: 0.5 mm
Circular groove having the same center of that of the nozzle hole
diameter: 3.0 mm.phi. depth: 3 mm
______________________________________
The extruded fiber is spread by a plate of a vinyl chloride
inclined by 45.degree. to the extruded fibers at a position remote
from the spinneret by about 20 mm, and the spread fiber is
collected on a metal wire net of 10 mesh.
The main spinning conditions and characteristics of the obtained
fiber are shown in Table 5.
It is apparent that the Mw/Mn and MFR of the polypropylene in the
dopes one within the range defined by the present invention, from
the value of Mw/Mn and MFR of the fibers shown in Table 5. Further,
the microwave birefringence, Mw/Mn, and MFR of the fibers in
Example 11 and 12 are also with in the range defined by the present
invention, and thus a polypropylene three-dimensional
plexifilamentary fiber having a superior spreadability and high
tensile strength is obtained.
TABLE 5 ______________________________________ Example 11 Example
12 2,2-dichloro-1,1,1- 1,2-dichloro- trifluoroethane
trifluoroethane ______________________________________
Concentration of 10.5 10.5 Polymer (wt %) Heating Time 65 59 (min)
Solution Temperature 215 215 (.degree.C.) Pressure 178 170
(kg/cm.sup.2 G) Pressure in 136 129 Pressure Let-down Chamber
(kg/cm.sup.2 G) Characteristics of Fiber Type of Fibers Fiber
Before Spread Fiber Before Spread Spreading Fiber Spreading Fiber
Fiber Spreadability a) -- .smallcircle. -- .smallcircle. Fineness
(d) 107 125 75 102 Tensile Strength 3.6 4.3 3.4 3.8 (g/d)
Elongation (%) 42 54 62 67 Specific Surface 7.7 8.5 Area (m.sup.2
/g) Microwave 0.120 0.109 Birefringence -- Mw/-- Mn 4.0 3.8 MFR 4.3
7.6 ______________________________________ a) Visual Evaluation o:
Good
EXAMPLES 13 TO 15
An isotactic polypropylene (E1100 supplied by Asahi Kasei Kogyo
Kabushiki Kaisha) having MFR of 0.50 is degradated by Perkadox 14
to prepare an isotactic polypropylene able to be used as a raw
material when manufacturing the fibers in Examples 13 to 15, and
having predetermined MFR and Mw/Mn values, respectively.
The preparation of the dopes and the flash spinning thereof in
Examples 13 to 15 are performed by the same apparatus as that used
in Examples 1 to 3, and by using 2,2-dichloro-1,1,1-trifluoroethane
or 1,2-dichlorotrifluoroethane.
The main spinning conditions and characteristics of the obtained
fibers are shown in Table 6.
It is apparent that the dope having the characteristics within the
range defined by the present invention can be prepared by the raw
material of the polypropylene within the range defined by the
present invention, from Table 6, and as a result, a fiber having a
superior fiber spreadability and high tensile strength can be
obtained.
When the 2,2-dichloro-1,1,1-trifluoroethane is used as the solvent,
the extruding volume of the solution per a cross section of the
spinning nozzle hole becomes twice that where
trichlorofluoromethane is used as the solvent, by suitably
selecting the spinning condition.
The fiber in Example 15 is spread, dispersed and piled one on the
other by the same method as that used in Example 7, to make a web.
The obtained web has a uniform thickness and a superior
appearance.
TABLE 6 ______________________________________ Example 13 14 15
______________________________________ Solvent a) TCFM DCTFE DCTFE
Polymer Used as Raw Material MFR 3.5 3.6 3.8 -- Mw/-- Mn 4.4 4.3
4.2 Concentration of Polymer 10.6 10.3 10.3 (wt %) Extruding Volume
(g/min) Solution 2153 2332 2276 Polymer 228 240 234 Condition in
Position Where Polymer is dissolved Temperature (.degree.C.) 229
225 227 Pressure (kg/cm.sup.2 G) 200 173 164 Condition in Pressure
Let-down Chamber Temperature (.degree.C.) 195 210 209 Pressure
(kg/cm.sup.2 G) 54 96 108 Dimension of Spinning Head Pressure
Let-down Orifice Diameter (mm) 0.70 0.85 0.85 Length (mm) 5.0 5.0
5.0 Spinning Nozzle Hole Diameter (mm) 0.95 0.70 0.70 Length (mm)
0.95 0.70 0.70 Groove of Nozzle Diameter (mm) 6.4 4.7 4.7 Length
(mm) 5.3 4.1 4.1 Extruding Volume at Spinning Nozzle Hole (g/Sec
.multidot. mm.sup.2) Solution 50.6 101 98.6 Polymer 5.4 10.4 10.1
Fiber Spreadability b) .smallcircle. .smallcircle. .smallcircle.
Characteristics of Spread Fiber MFR 7.3 3.8 4.6 -- M/-- Mn 3.9 4.2
4.1 Microwave Birefringence 0.093 0.104 0.095 Fineness (d) 184 181
201 Tensile Strength (g/d) 3.0 3.9 3.2 Specific Surface Area
(m.sup.2 /g) 10 11 11 ______________________________________ a)
TCFM: trichlorofluoromethane, DCTFE:
2,2dichloro-1,1,1-trifluoroethane b) Visual Evaluation o: Good
EXAMPLE 16
A polypropylene solution in Example 16 is prepared by an autoclave.
Namely 64.1 g of an isotactic polypropylene having MFR of 1.3 and
546 g of a blended solvent composed of a dichloromethane of 38.5 wt
% and a 2,2-dichloro-1,1,1-trifluoroethane of 61.5 wt % are fed
into the autoclave so that a concentration of the polypropylene
becomes 10.5 wt %. The autoclave is heated with a rotation of a
propeller type stirring machine to dissolve the polypropylene in
the solvent. The solution is further heated, and thus a pressure of
the solution is raised to completely dissolve the polypropylene.
After completing the dissolution of the polypropylene, the solution
is partially exhausted from a nozzle arranged on a bottom of the
autoclave so that the pressure of the solution does not exceed 300
kg/cm.sup.2 G, which is a design pressure of the autoclave, and
thus the pressure of the solution is kept between 200 kg/cm.sup.2 G
and 300 kg/cm.sup.3 G. When the temperature of the solution becomes
215.degree. C. after heating for 53 min, the solution is exhausted
so that the pressure of the solution is kept at a pressure lower
than the pressure, i.e., 100 kg/cm.sup.2 G used at spinning process
by 10 kg/cm.sup.2 G. When the temperature of the solution becomes
again at 215.degree. C., the stirring machine is stopped, N.sub.2
gas is introduced from a N.sub.2 gas introducing valve arranged on
an upper portion of the autoclave, to keep the pressure of the
solution at the pressure of 100 kg/cm.sup.2 G, and simultaneously,
an exhausting valve arranged on the bottom of the autoclave is
opened to exhaust the solution through a pressure let-down orifice
having a diameter of 0.65 mm and length of 5 mm, into a pressure
let-down chamber having a diameter of 8 mm and length of 40 mm.
Then the solution is introduced into a spinneret having the
following specification, and extruded into the atmosphere.
An angle of introducing the solution from the pressure let-down
chamber to
______________________________________ a nozzle hole of the
spinneret: 60.degree. Nozzle Hole diameter: 0.5 mm length: 0.5 mm
Circular groove having the same center of that of the nozzle hole
diameter: 3.0 mm.phi. depth: 3 mm
______________________________________
The extruded fiber is spread by a plate of a vinyl chloride
inclined by 45.degree. to the extruded fibers at a position remote
from the spinneret by about 20 mm, and the spread fiber is
collected on a metal wire net of 10 mesh. In this case, the
pressure of the pressure let-down chamber is 77 kg/cm.sup.2 G.
The fiber before applying the spreading operation has a fineness of
72d, tensile strength of 3.9 g/d, elongation of 47% MFR of 4.5, and
Mw/Mn of 4.1, and the spread fiber has a fineness of 81 d, tensile
strength of 4.0 g/d, elongation of 55%, microwave birefringence of
0.101, and specific surface area of 12.7 m.sup.2 /g. Thus, the
polypropylene three-dimensional plexifilamentary fiber having a
superior configuration can be obtained.
EXAMPLE 17
A polypropylene solution in Example 17 is also prepared by the
autoclave. Namely 64.1 g of an isotactic polypropylene having an
MFR of 1.3 and 546 g of a blended solvent composed of a
dichloromethane of 33 wt % and a 1.2-dichloro-trifluoroethane of 67
wt % are supplied into the autoclave so that a concentration of the
polypropylene becomes 10.5 wt %. A dope is prepared under a high
temperature and a high pressure and a fiber is spun and spread by
the same operations as used in Example 16, except that the pressure
of the solution is 103 kg/cm.sup.2 G and the pressure in the
pressure let-down chamber is 85 kg/cm.sup.2 G.
The spread fiber has a fineness of 68 d, tensile strength of 4.3
g/d, fiber width of 25 mm, microwave birefringence of 0.115, Mw/Mn
of 3.6, MFR of 5.5, and specific surface area of 12.7 m.sup.2 /g.
Thus, a highly spread polypropylene three-dimensional
plexifilamentary fiber having a superior configuration can be
obtained.
* * * * *